RF power amplifier

ABSTRACT

A reduction is achieved in the primary-side input impedance of a transformer (voltage transformer) as an output matching circuit without involving a reduction in Q-factor. An RF power amplifier includes transistors, and a transformer as the output matching circuit. The transformer has a primary coil and a secondary coil which are magnetically coupled to each other. To the input terminals of the transistors, respective input signals are supplied. The primary coil is coupled to each of the output terminals of the transistors. From the secondary coil, an output signal is generated. The primary coil includes a first coil and a second coil which are coupled in parallel between the respective output terminals of the transistors, and each magnetically coupled to the secondary coil. By the parallel coupling of the first and second coils of the primary coil, the input impedance of the primary coil is reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2008-290911 filed onNov. 13, 2008 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to RF power amplifiers, and particularlyto a technology which is effective in reducing the input impedance of aprimary coil in a transformer of an impedance matching circuit withoutinvolving a reduction in Q-factor.

As has been well known, in a radio-frequency (RF) power amplifiermounted in a communication device such as a mobile phone terminal deviceor a wireless LAN terminal, an impedance matching circuit is coupledbetween a source-grounded or emitter-grounded power amplificationtransistor and a load for the purpose of efficiently driving the antennaof the load with the power amplification transistor. The impedancematching circuit transforms a low output impedance of several ohms ofthe power amplification transistor to a high input impedance oftypically 50 ohms of the load. The impedance matching circuit is formedof passive elements which are a coil and a capacitor, and can be formedof a voltage transformer (transformer) having no loss and apredetermined transformation ratio. The primary coil of the transformeris coupled to the drain or collector of the power amplificationtransistor, while the secondary coil of the transformer is coupled tothe antenna of the load.

In Non-Patent Document 1 listed below, a high-efficiency class-Bpush-pull power amplifier is described in which, in an impedancematching circuit using a transformer, one end and the other end of theprimary coil of the transformer are coupled to a pair of N-channel MOStransistors driven by a complementary pair of input signals. To themidpoint of the primary coil, a drain power supply voltage is supplied,and the secondary coil of the transformer is coupled to a load.

In Non-Patent Document 2 listed below, a monolithic RF power amplifieris described in which a first on-chip transformer as an input balun,second and third on-chip transformers as a driver stage and aninter-stage matching circuit, and a power output stage are integrated ona silicon chip. The driver stage includes a pair of driver transistorsthat are driven by respective signals from both ends of the secondarycoil of the first on-chip transformer. The power output stage includes apair of output transistors that are driven by respective signals fromboth ends of the secondary coils of the second and third on-chip voltagetransformers. To each of the collectors of the pair of drivertransistors, a power supply voltage is supplied via the primary coil ofeach of the second and third on-chip transformers. The three on-chiptransformers are each formed of three-layer wiring over the siliconchip. To each of the collectors of the pair of driver transistors in thedriver stage, an output matching circuit formed of a plurality of coilsand a plurality of capacitors which are external members of the siliconchip is coupled.

In Non-Patent Document 3 listed below, there is described a poweramplifier for solving a problem associated with the output matchingcircuit formed of the external members of the monolithic RF poweramplifier described in Non-Patent document 2 listed below, and alsosolving the problems of low breakdown voltage and heat dissipation of ashort-channel MOS transistor. The power amplifier is called adistributed active-transformer (DAT) power amplifier by the authors ofNon-Patent document 3. The primary coil of the distributedactive-transformer (DAT) is formed of a plurality of slab inductorsarranged in an annular configuration, and each having a high Q-factor.Between the plurality of inductors, differential push-pull amplifierseach including a pair of N-channel MOS transistors driven by acomplementary pair of input signals are coupled. In the primary coil ofthe distributed active-transformer (DAT), the plurality of inductors andthe plurality of differential push-pull amplifiers are alternatelyarranged along the annular configuration. The secondary coil of thedistributed active-transformer (DAT) is formed of a 1-turn metal stripinside the primary coil having the annular shape. Since the plurality ofdifferential push-pull amplifiers of the primary coil allow flows ofidentical synchronized alternating currents, a magnetic field is inducedin the secondary coil so that the sum of the differential voltages ofthe plurality of differential push-pull amplifiers is generated. Asmentioned above, DAT is the abbreviation of the distributedactive-transformer.

The DAT power amplifier described in Non-Patent Document 3 listed belowalso includes, in order to supply the complementary pair of inputsignals to the respective gates of each of the MOS transistors of theplurality of differential push-pull amplifiers, differential signallines for supplying a balanced signal from the outside of the annularshape to the center portion of the annular shape in order to supply thecomplementary pair of input signals to the respective gates of the pairof MOS transistors of each of the plurality of differential push-pullamplifiers. Between the center portion and each of the respective gatesof the pair of MOS transistors, a distribution circuit for symmetricalcoupling is disposed. Note that, since the primary coil having theannular shape of the distributed active-transformer (DAT) is formed ofthe plurality of slab inductors each having a linear shape, each of theslab inductors has a Q-factor higher than that of a typical spiralinductor in which a negative mutual inductance is generated by currentflowing in opposing wires.

In Non-Patent Document 4 listed below, it is stated that the circularstructure of a distributed active-transformer (DAT) of a DAT poweramplifier as described in Non-Patent Document 3 listed below serves as afactor causing cross coupling of an input and an output of power whichdestabilizes the amplifier. In Non-Patent Document 4 listed below, it isalso stated that the power coupling structure of the distributedactive-transformer (DAT), which is rather large compared with activedevices, determines the total chip size, and hence is not desirable interms of cost. Therefore, in Non-Patent Document 4 listed below, inorder to reduce the linking of the input and the output for the sake ofstability, input ports coupled to power devices are disposed at theportion of the primary coil corresponding to one side of thequadrilateral of the distributed active-transformer (DAT), while theoutput port of the secondary coil of the distributed active-transformer(DAT) is disposed at the opposite side of the quadrilateral thereof.

Non-Patent Document 1

-   Frederic H. Raab et al, “RF and Microwave Power Amplifier and    Transmitter Technologies-Part 2”, High Frequency Electronics, PP.    22-36, May 2003.

Non-Patent Document 2

-   Werner Simburger et al., “A Monolithic Transformer Coupled 5-W    Silicon Power Amplifier with 59% PAE at 0.9 GHz”, IEEE JOURNAL OF    SOLID-STATE CIRCUITS, VOL. 34, NO. 12 DECEMBER 1999, PP. 1881-1892.

Non-Patent Document 3

-   Ichiro Aoki et al., “Fully Integrated CMOS Power Amplifier Design    Using the Distributed Active-Transformer Architecture”, IEEE JOURNAL    OF SOLID-STATE CIRCUITS, VOL. 37, NO. 3, March 2002, PP. 371-383.

Non-Patent Document 4

-   Kyu Hwan An et al, “A Monolithic Voltage-Boosting Parallel-Primary    Transformer Structures for Fully Integrated CMOS Power Amplifier    Design”, 3 to 5 Jun. 2007, 2007 IEEE Radio Frequency Integrated    Circuits Symposium, PP. 419 to 422.

SUMMARY OF THE INVENTION

Prior to the present invention, the present inventors undertook thedevelopment of an RF power amplifier using a voltage transformer(transformer) having no loss and a predetermined transformation ratio asan output impedance matching circuit. Because the RF power amplifier wasto be mounted in a mobile phone terminal device, the development task ofachieving a size reduction and low cost was given to the presentinventors.

In the process of the development, the present inventors first conducteda detailed examination of the background technology.

FIG. 1 shows the power amplifier examined by the present inventors basedon the DAT power amplifier described in Non-Patent Document 3 listedabove prior to the present invention. The power amplifier uses atransformer formed on a silicon (Si) chip (on-chip transformer). Thetransformer is a device which performs energy transfer between aplurality of wires placed in generally parallel and proximate relationusing electromagnetic induction. The power amplifier shown in the planview of FIG. 1 includes one transformer and a plurality of transistorseach formed on one Si chip, and performs power combining and impedancematching for output power using the transformer.

The power amplifier uses, as active devices, eight source-groundedN-channel MOS transistors 7A to 7H that can be manufactured by a CMOSmanufacturing process. The respective input terminals, output terminals,and ground terminals of the individual transistors serve as therespective gates, drains, and sources thereof. As an output matchingcircuit and a power combining circuit, an on-chip transformer is usedwhich includes a plurality of (four) metal wires 1A to 1D as a primarycoil having an annular shape, and a metal thin-film wire 2 as a 1-turnmetal strip of a secondary coil inside the primary coil. Between thefirst metal wire 1A and the second metal wire 1B, a first push-pullpower amplification circuit including the pair of N-channel MOStransistors 7A and 7B and a capacitor 4A is coupled. To the respectivegates of the transistors 7A and 7B, a non-inverted input signal +Inputand an inverted input signal −Input are supplied respectively. Betweenthe second metal wire 1B and the third metal wire 1C, a second push-pullpower amplification circuit including the pair of N-channel MOStransistors 7C and 7D and a capacitor 4B is coupled. Between the thirdmetal wire 1C and the fourth metal wire 1D, a third push-pull poweramplification circuit including the pair of N-channel MOS transistors 7Eand 7F and a capacitor 4C is coupled. Finally, between the fourth metalwire 1D and the first metal wire 1A, a fourth push-pull poweramplification circuit including the pair of N-channel MOS transistors 7Gand 7H and a capacitor 4D is coupled. The four metal wires 1A to 1D asthe primary coil having the annular shape are formed of a plurality ofslab inductors each having a high Q-factor, and a drain power supplyvoltage Vdd is supplied to each of the midpoints thereof. From the bothends of the metal thin-film wire 2 as the 1-turn metal strip of thesecondary coil inside the primary coil, an output signal Output isgenerated, and a capacitor 4E is coupled to the both ends. Note that thecapacitors 4A to 4D are for reducing the levels of odd-numberedharmonics in the push-pull power amplification circuits.

In the power amplifier shown in the plan view of FIG. 1, the four slabinductors as the primary coil having the annular shape and the fourpush-pull power amplification circuits are alternately arranged in anannular configuration, and the primary coil and the secondary coil 2having the annular shape are disposed adjacent to each other, andmagnetically coupled. As a result, the outputs of the four push-pullpower amplification circuits are power-combined by the on-chiptransformer, and output matching can be performed. In addition, theproblem of low breakdown voltage and heat dissipation of a short-channelMOS transistor can be solved. Further, there is achieved an effect ofallowing compact formation of the output matching circuit of the poweramplifier on the Si chip, and thereby allowing significant reductions inthe manufacturing cost and size of the power amplifier. Furthermore,since the pair of MOS transistors of each of the push-pull poweramplification circuits perform differential operations, the currents inthe pair of MOS transistors are cancelled out to stabilize sourcevoltages, and also stabilize the drain power supply voltage Vdd at eachof the midpoints of the four slab metal wires 1A to 1D. Consequently,there is also achieved an effect of eliminating the need for largecapacitors for voltage stabilization, and allowing reductions in themanufacturing cost and size of the power amplifier.

FIG. 2 also shows another power amplifier examined by the presentinventors based on the DAT power amplifier described in Non-PatentDocument 3 listed above prior to the present invention. The poweramplifier shown in FIG. 2 is different from the power amplifier shown inFIG. 1 in the following point. That is, in the power amplifier shown inFIG. 2, eight metal wires 1A to 1H as a primary coil having an outerannular shape are arranged outside the secondary coil 2 having theannular shape of the on-chip transformer, and four metal wires 1I to 1Lare arranged as a primary coil having an inner annular shape inside thesecondary coil 2. Between the outer metal wire 1A and the outer metalwire 1B, a push-pull power amplification circuit including a pair ofN-channel MOS transistors 3A and 3B and the capacitor 4A is coupled. Tothe respective gates of the transistors 3A and 3B, the non-invertedinput signal +Input and the inverted input signal −Input are suppliedrespectively. Between the outer metal wire 1C and the outer metal wire1D, a push-pull power amplification circuit including a pair ofN-channel MOS transistors 3C and 3D and the capacitor 4B is coupled.Between the outer metal wire 1E and the outer metal wire 1F, a push-pullpower amplification circuit including a pair of N-channel MOStransistors 3E and 3F and the capacitor 4C is coupled. Finally, betweenthe outer metal wire 1G and the outer metal wire 1H, a push-pull poweramplification circuit including a pair of N-channel MOS transistors 3Gand 3H and the capacitor 4D is coupled.

To the midpoint of the inner metal wire 1L located above and rightwardof the center portion of the annular shape, the drain power supplyvoltage Vdd is supplied. The inner metal wire 1L has at the upper leftone end thereof which is coupled to the drain of the N-channel MOStransistor 3A via a bonding wire 8A and the outer metal wire 1A, and thelower right other end thereof which is coupled to the drain of theN-channel MOS transistor 3F via a bonding wire 8H and the outer metalwire 1F. To the midpoint of the inner metal wire 1I located above andleftward of the center portion of the annular shape also, the drainpower supply voltage Vdd is supplied. The inner metal wire 1I has at thelower left one end thereof which is coupled to the drain of theN-channel MOS transistor 3C via a bonding wire 8C and the outer metalwire 1C, and the upper right other end thereof which is coupled to thedrain of the N-channel MOS transistor 3H via a bonding wire 8B and theouter metal wire 1H. To the midpoint of the inner metal wire 1J locatedbelow and leftward of the center portion of the annular shape also, thedrain power supply voltage Vdd is supplied. The inner metal wire 1J hasat the lower right one end thereof which is coupled to the drain of theN-channel MOS transistor 3E via a bonding wire 8E and the outer metalwire 1E, and the upper left other end thereof which is coupled to thedrain of the N-channel MOS transistor 3B via a bonding wire 8D and theouter metal wire 1B. To the midpoint of the inner metal wire 1K locatedbelow and rightward of the center portion of the annular shape, thedrain power supply voltage Vdd is supplied. The inner metal wire 1K hasat the upper right one end thereof which is coupled to the drain of theN-channel MOS transistor 3G via a bonding wire 8G and the outer metalwire 1G, and the lower left other end thereof which is coupled to thedrain of the N-channel MOS transistor 3D via a bonding wire 8F and theouter metal wire 1D.

FIG. 3 also shows still another power amplifier examined by the presentinventors based on the DAT power amplifier described in Non-PatentDocument 3 listed above prior to the present invention. The poweramplifier shown in FIG. 3 is different from the power amplifier shown inFIG. 2 in that the number of the metal wires of the primary coil eachlocated outside the secondary coil 2 and having an outer annular shape,and the number of the metal wires of the primary coil each locatedinside the secondary coil 2 and having an inner annular shape have beeneach reduced to one-half, and the number of the push-pull poweramplification circuits has been also reduced to one-half. That is, inthe power amplifier shown in FIG. 3, the four metal wires 1A to 1D asthe primary coil each having the outer annular shape are arrangedoutside the secondary coil 2 having the annular shape of the on-chiptransformer, and the two metal wires 1E and 1F as the primary coil eachhaving the inner annular shape are arranged inside the secondary coil 2.

To the midpoint of the inner metal wire 1E located over the centerportion of the annular shape, the drain power supply voltage Vdd issupplied. The inner metal wire 1E has at the lower left one end thereofwhich is coupled to the drain of the N-channel MOS transistor 3C via thebonding wire 8A and the outer metal wire 1B, and the lower right otherend thereof which is coupled to the drain of the N-channel MOStransistor 3D via the bonding wire 8D and the outer metal wire 1C. Tothe midpoint of the inner metal wire 1F located under the center portionof the annular shape also, the drain power supply voltage Vdd issupplied. The inner metal wire 1F has at the upper right one end thereofwhich is coupled to the drain of the N-channel MOS transistor 3B via thebonding wire 8C and the outer metal wire 1D, and the upper left otherend thereof which is coupled to the drain of the N-channel MOStransistor 3A via the bonding wire 8B and the outer metal wire 1A.

It has been revealed that the power amplifiers examined by the presentinventors prior to the present invention, and shown in FIGS. 2 and 3have problems as described below. That is, as described in Non-PatentDocument 4 listed above, the annular shape of each of the on-chiptransformers shown in FIGS. 2 and 3 serves as a factor causing crosscoupling of the input and output of power which destabilizes theamplifiers. Specifically, in the power amplifier shown in FIG. 2, thefollowing is required to supply the complementary pair of input signals+Input and −Input in parallel to the respective gates of the pluralityof pairs of MOS transistors 3A, 3B, . . . 3G, and 3H of the plurality ofdifferential push-pull amplifiers. First, differential signal lines forsupplying a balanced signal of the complementary pair of input signals+Input and −Input from the outside of the metal wires 1A and 1B, . . .1G, and 1H as the primary coil each having the outer annular shape tothe center portion of the annular shape are required. Next, thedistribution circuits having a plurality of symmetrical coupled wiresare required between the center portion of the annular shape and therespective gates of the plurality of pairs of MOS transistors 3A, 3B, .. . 3G, and 3H. However, the differential signal lines for supplying thebalanced signal of the complementary pair of input signals +Input and−Input from the outside of the annular shape to the center portion ofthe annular shape in the inside thereof form cross wires with thesecondary coil 2 having the annular shape so that signal loss occurs atthe portions of the cross wires. In addition, the plurality ofsymmetrically coupled wires of the distribution circuits which arecoupled to the center portion of the annular shape and to the respectivegates of the plurality of pairs of MOS transistors also form cross wireswith the secondary coil 2 having the annular shape so that signal lossoccurs at the portions of the cross wires. As a result of simulationperformed by the present inventors, it has been proved that the lossreduces power added efficiency (PAE) by 5%.

Further in the power amplifier shown in FIG. 2, it is necessary to formthe on-chip transformer and the plurality of MOS transistors 3A, 3B, . .. 3G, and 3H of the plurality of differential push-pull amplifiers onthe same Si chip. Compared with the chip area occupied by the MOStransistors 3A, 3B, . . . 3G, and 3H, the chip area occupied by theon-chip transformer having the annular shape increases to increase themanufacturing cost of the power amplifier. Furthermore, the problems ofthe deterioration of the power added efficiency due to the loss and highmanufacturing cost cannot be circumvented even with the power amplifiershown in FIG. 3.

FIG. 4 shows a power amplifier examined by the present inventors basedon the DAT power amplifier described in Non-Patent Document 4 listedabove prior to the present invention. In the power amplifier shown inFIG. 4, in order to reduce the coupling between the input and output forthe sake of stability, the input ports coupled to the power devices aredisposed in the primary coil at the lower side of the quadrilateral ofthe transformer, while the output port of the secondary coil of thetransformer is disposed at the upper opposite side of the quadrilateralthereof. The secondary coil having the annular shape of the transformerincludes an outer secondary coil 2A and an inner secondary coil 2B. Oneend of the outer secondary coil 2A which is located leftward of themiddle of the upper side of the quadrilateral is coupled to an outputterminal Output, while the other end thereof which is located rightwardof the middle of the upper side of the quadrilateral is coupled to oneend of the inner secondary coil 2B which is located leftward of themiddle of the upper side of the quadrilateral via a lower-layer crosswire 5H. The other end of the inner secondary coil 2B which is locatedrightward of the middle of the upper side of the quadrilateral iscoupled to a ground voltage GND via a lower-layer cross wire 5D.

The first primary coil having the annular shape of the transformerincludes the metal wire 1A as a long-distance wire extending inprotruding relation to form the left side of the quadrilateral, alower-layer cross wire 5F located at the middle of the lower side of thequadrilateral, and the metal wire 1B as a short-distance wire locatedleftward of the middle of the lower side of the quadrilateral. That is,one end of the metal wire 1A as the long-distance wire extending inprotruding relation to form the left side of the quadrilateral which islocated rightward of the middle of the lower side of the quadrilateraland one end of the metal wire 1B as the short-distance wire which islocated leftward of the middle of the lower side of the quadrilateralare coupled to each other via the lower-layer cross wire 5F. The otherend of the metal wire 1B as the short-distance wire is coupled to thedrain of the N-channel MOS transistor 7B, while the other end of themetal wire 1A as the long-distance wire which is located leftward of themiddle of the lower side of the quadrilateral is coupled to the drain ofthe N-channel MOS transistor 7A. The second primary coil having theannular shape of the transformer includes the metal wire 1D as along-distance wire extending in protruding relation to form the rightside of the quadrilateral, a lower-layer cross wire 5G located at themiddle of the upper side of the quadrilateral, the metal wire 1C as along-distance wire located in an inner left portion of thequadrilateral, a lower-layer cross wire 5E located at the middle of thelower side of the quadrilateral, and the metal wire 1E as ashort-distance wire located rightward of the middle of the lower side ofthe quadrilateral. That is, one end of the metal wire 1D as thelong-distance wire extending in protruding relation to form the rightside of the quadrilateral which is located rightward of the middle ofthe lower side of the quadrilateral is coupled to the drain of theN-channel MOS transistor 7D, while the other end of the metal wire 1D asthe long-distance wire which is located rightward of the middle of theupper side of the quadrilateral is coupled to one end of the metal wire1C as the long-distance wire located in the inner left portion of thequadrilateral which is located leftward of the middle of the upper sideof the quadrilateral via the lower-layer cross wire 5G. The other end ofthe metal wire 1C as the long-distance wire which is located leftward ofthe middle of the lower side of the quadrilateral is coupled to thedrain of the N-channel MOS transistor 7C via the lower-layer cross wire5E located at the middle of the lower side of the quadrilateral and viathe metal wire 1E as the short-distance wire located rightward of themiddle of the lower side of the quadrilateral. To the respective drainsof the N-channel MOS transistors 7A, 7B, 7C, and 7D, the drain powersupply voltage Vdd is supplied via bonding wires 9A, 9B, 9C, and 9D.

In the power amplifier shown in FIG. 4, gate complementary input signalwires for supplying the complementary pair of input signals +Input and−Input to the respective gates of the plurality of MOS transistors 7A,7B, 7C, and 7D need not form cross wires with the outer secondary coil2A and the inner secondary coil 2B of the transformer. Also, the gatecomplementary input signal wires of the MOS transistors 7A . . . 7D neednot form cross wires with the bonding wires 9A . . . 9D in accordancewith the device layout of the Si chip. Therefore, in the power amplifiershown in FIG. 4, it is possible to solve the problem of instability dueto the cross coupling of the input and the output of power of each ofthe differential push-pull amplifiers or of the deterioration of thepower added efficiency. Moreover, in the power amplifier shown in FIG.4, the transformer and the plurality of MOS transistors 7A . . . 7D ofthe plurality of differential push-pull amplifiers need not be formed onthe same Si chip. While the MOS transistors 7A . . . 7D are formed on aSi chip, the transformer having the annular shape can be formed on aprinted wiring substrate which is lower in cost than the Si chip. Sincethe transformer having the annular shape, and formed on the printedwiring substrate and the MOS transistors 7A . . . 7D formed on the Sichip can be coupled to each other by the bonding wires, themanufacturing cost of the power amplifier can be reduced.

However, the examination conducted by the present inventors has revealedthe problem that, in the power amplifier shown in FIG. 4, the inputimpedance of the primary coils of the transformer increases. That is, inthe power amplifier shown in FIG. 4, the lengths of the first primarycoil (the wire 1A, the cross wire 5F, and the wire 1B) and the secondprimary coil (the wire 1D, the cross wire 5G, the wire 1C, the crosswire 5E, and the wire 1E) are each generally equal to the perimeter ofthe annular shape of the transformer. Both ends of the first primarycoil are coupled to the respective drains of the MOS transistors 7A and7B of the first differential push-pull amplifier. Both ends of thesecond primary coil are coupled to the respective drains of the MOStransistors 7C and 7D of the second differential push-pull amplifier.The value of the input impedance of the primary coils is directlyproportional to the length of each of the primary coils, i.e., to theperimeter of the annular shape. In the transformer shown in FIG. 4, thenumber of the differential push-pull amplifiers arranged around theannular shape is smaller than that in each of the transformers of thepower amplifiers shown in FIGS. 1 and 2. Accordingly, the length of eachof the primary coils between the respective drains of the two MOStransistors of one differential push-pull amplifier and the inputimpedance thereof increase.

When the input impedance of the primary coils of the transformerincreases relative to the output impedance (of about several ohms) ofthe drain of each of the MOS transistors of the differential push-pullamplifier, matching conditions in output impedance matching performed bythe transformer cannot be obtained. By reducing the radius and perimeterof the annular shape of the transformer, the input impedance of theprimary coils of the transformer can be reduced. However, theexamination conducted by the present inventors has revealed that, sincethe transformer consequently operates generally as a spiral inductor,the problem of a reduction in Q-factor occurs, as described inNon-Patent Document 4 listed above.

The present inventors have also discovered the problem that, in thetransformer shown in FIG. 4, signal loss also occurs in the bondingwires 9A, 9B, 9C, and 9D for supplying the drain power supply voltageVdd to the respective drains of the N-channel MOS transistors 7A, 7B,7C, and 7D, and hence the power added efficiency (PAE) of the amplifiedRF output signal deteriorates.

Further, in the transformer shown in FIG. 4, the radius and perimeter ofthe annular shape of the first primary coil (the wire 1A, the cross wire5F, and the wire 1B) are larger on the left-hand side of thequadrilateral than on the right-hand side thereof. By contrast, theradius and perimeter of the annular shape of the second primary coil(the wire 1D, the cross wire 5G, the wire 1C, the cross wire 5E, and thewire 1E) are larger on the right-hand side of the quadrilateral than onthe left-hand side thereof. As a result, a subsidiary problem has beenrevealed that even-numbered harmonic distortion in the amplified RFoutput signal generated from the output terminal Output of each of thesecondary coils 2A and 2B increases to cause the deterioration of anadjacent channel leakage power ratio (ACPR) and the power addedefficiency (PAE). As shown above, ACPR is the abbreviation of theadjacent channel leakage power ratio.

The present invention has been achieved as a result of the foregoingexamination conducted by the present inventors prior to the presentinvention.

It is therefore an object of the present invention to provide an RFpower amplifier in which the primary-side input impedance of thetransformer can be reduced without involving a reduction in Q-factor.

Another object of the present invention resides in reducing thedeterioration of the power added efficiency (PAE) of the amplified RFoutput signal. An additional object of the present invention resides inreducing an increase in harmonic distortion in the RF power amplifier.

The above and other objects and novel features of the present inventionwill become apparent from the description of the present specificationand the accompanying drawings.

As shown below, a brief description will be given of representativeaspects of the invention disclosed in the present application.

That is, a representative RF power amplifier of the present inventionincludes first and second transistors (3A and 3B) each as an activedevice of a push-pull power amplification circuit, and a transformer(1A, 1B, and 2) as an output matching circuit.

Input signals (+Input and −Input) are supplied to the respective inputterminals of the first and second transistors (3A and 3B).

The transformer has a primary coil (1A and 1B) and a secondary coil (2)which are magnetically coupled.

The primary coil (1A and 1B) of the transformer is coupled to each ofthe output terminals of the first and second transistors (3A and 3B),and an output signal (Output) is generated from the secondary coil (2)of the transformer.

The primary coil (1A and 1B) of the transformer includes at least afirst coil (1A) and a second coil (1B) which are coupled in parallelbetween the respective output terminals of the first and secondtransistors (3A and 3B), and each is magnetically coupled to thesecondary coil (2) (see FIG. 9).

The following is a brief description of effects obtained by therepresentative aspects of the invention disclosed in the presentapplication.

That is, an RF power amplifier can be provided in which the primary-sideinput impedance of a transformer can be reduced without involving areduction in Q-factor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a power amplifier examined by the present inventors basedon the DAT power amplifier described in Non-Patent Document 3 prior tothe present invention;

FIG. 2 also shows another power amplifier examined by the presentinventors based on the DAT power amplifier described in Non-PatentDocument 3 prior to the present invention;

FIG. 3 also shows still another power amplifier examined by the presentinventors based on the DAT power amplifier described in Non-PatentDocument 3 prior to the present invention;

FIG. 4 shows a power amplifier examined by the present inventors basedon the DAT power amplifier described in Non-Patent Document 4 prior tothe present invention;

FIGS. 5(A) to 5(D) are views each showing a basic configuration of an RFpower amplifier according to an embodiment of the present invention;

FIG. 6 is a view showing another configuration of the RF power amplifieraccording to the embodiment of the present invention;

FIG. 7 is a view showing still another configuration of the RF poweramplifier according to the embodiment of the present invention;

FIG. 8 is a view showing yet another configuration of the RF poweramplifier according to the embodiment of the present invention;

FIG. 9 is a view showing still another configuration of the RF poweramplifier according to the embodiment of the present invention;

FIG. 10 is a view showing yet another configuration of the RF poweramplifier according to the embodiment of the present invention;

FIG. 11 is a view showing a configuration of a monolithic RF poweramplifier according to another embodiment of the present invention, inwhich the transformer and N-channel MOS transistors of one push-pullpower amplification circuit, each illustrated in FIG. 5, are integratedin a Si chip;

FIG. 12 is a view showing a configuration of an RF power amplifiermodule according to sill another embodiment of the present invention, inwhich the Si chip having the N-channel MOS transistors of the onepush-pull power amplification circuit integrated therein and the outputimpedance matching transformer illustrated in FIG. 9 are embedded;

FIG. 13 is a plan view of a silicon chip showing a layout of variousdevices forming a semiconductor integrated circuit according to theembodiment of the present invention shown in FIG. 12;

FIG. 14 is a view showing a configuration of an RF power amplifiermodule according to yet another embodiment of the present invention, inwhich a GaAs chip having a high-breakdown-voltage npn-typeheterojunction bipolar transistor integrated therein as each of thetransistors of the push-pull power amplification circuit and the outputimpedance matching transformer illustrated in FIG. 9 are embedded;

FIG. 15 is a view showing a configuration of an LDMOS transistor used ineach of the push-pull power amplification circuits of the RF poweramplifiers according to the various embodiments of the present inventionshown in FIGS. 5 to 13;

FIG. 16 is a view showing a structure of a typical LDMOS transistor fora comparison with the LDMOS transistor shown in the lowercross-sectional view of FIG. 15;

FIG. 17 is a view showing a configuration of the high-breakdown-voltagenpn-type heterojunction bipolar transistor used in the push-pull poweramplification circuit of the RF power amplifier according to the yetanother embodiment of the present invention shown in FIG. 14; and

FIG. 18 is a view showing a configuration of a specific RF poweramplifier module used in a mobile phone terminal to which any of thevarious embodiments of the present invention shown in FIGS. 5 to 17described above is applied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Representative Embodiment

First, a description will be given of an outline of representativeembodiments of the invention disclosed in the present application.Reference numerals in the drawings which are nestled in parentheses andreferenced in the description of the outline of the representativeembodiments are only illustrative of the content of the concept of thecomponents provided with the reference numerals.

1. An RF power amplifier according to a representative embodiment of thepresent invention includes a first transistor (3A) and a secondtransistor (3B) each as an active device of a push-pull poweramplification circuit, and a transformer (1A, 1B, and 2) as an outputmatching circuit of the push-pull power amplification circuit.

An input terminal of the first transistor (3A) and an input terminal ofthe second transistor (3B) can be respectively supplied with anon-inverted input signal (+Input) and an inverted input signal(−Input).

The transformer has a primary coil (1A and 1B) and a secondary coil (2)which are magnetically coupled.

One end and the other end of the primary coil (1A and 1B) of thetransformer are coupled respectively to an output terminal of the firsttransistor (3A) and an output terminal of the second transistor (3B),and an output signal (Output) can be generated from between one end andthe other end of the secondary coil (2) of the transformer.

The primary coil (1A and 1B) of the transformer includes at least afirst coil (1A) and a second coil (1B) which are coupled in parallelbetween the output terminal of the first transistor (3A) and the outputterminal of the second transistor (3B), and each is magnetically coupledto the secondary coil (2) (see FIG. 5(A)).

According to the embodiment described above, the primary coil (1A and1B) of the transformer includes at least the first coil (1A) and thesecond coil (1B) which are coupled in parallel. This allows a reductionin the primary-side input impedance of the transformer. In this case,since it is not necessary to reduce the radius and perimeter of theannular shape of the transformer, a reduction in Q-factor can beeliminated.

In a preferred embodiment, at least one of the first coil (1A) and thesecond coil (1B) can be supplied with a power supply voltage (Vdd)between the output terminal of the first transistor (3A) and the outputterminal of the second transistor (3B) (see FIG. 5(A)).

According to the preferred embodiment described above, it is notnecessary to use bonding wires as described in Non-Patent Document 4listed above when the power supply voltage (Vdd) is supplied to thefirst transistor (3A) and the second transistor (3B). The power supplyvoltage is supplied using the primary coil having a low impedance.Therefore, it is possible to reduce the problem of the deterioration ofthe power added efficiency due to signal loss in the bonding wiresdescribed in Non-Patent Document 4 listed above.

In another preferred embodiment, the primary coil (1A and 1B) and thesecondary coil (2) of the transformer are formed of respective metalthin-film wires having annular shapes, and each is formed flat over asurface of a substrate.

According to the another preferred embodiment described above, theheights of the members of the transformer can be reduced. This allows areduction in the size of a mobile phone terminal when the RF poweramplifier including the transformer is mounted in the mobile phoneterminal.

In still another preferred embodiment, the metal thin-film wire formingthe primary coil (1A and 1B) of the transformer is formed to have awidth larger than a width of the metal thin-film wire forming thesecondary coil (2) of the transformer.

In yet another preferred embodiment, the metal thin-film wire formingthe primary coil (1A and 1B) of the transformer and the metal thin-filmwire forming the secondary coil (2) of the transformer are formed aroundthe annular shapes.

The primary coil (1A and 1B) and the secondary coil (2) are set to apredetermined ratio of turns to allow the transformer to execute anoutput matching operation in accordance with an impedance transformationratio determined by the ratio of turns.

In a more preferred embodiment, the number of turns of the secondarycoil (2) is set to generally an integral multiple of the number of turnsof the primary coil (1A and 1B).

In a still more preferred embodiment, the first coil (1A) and the secondcoil (1B) of the primary coil (1A and 1B) of the transformer are formedrespectively of an outer metal thin-film wire and an inner metalthin-film wire each having the annular shape.

The secondary coil (2) is formed of a middle metal thin-film wire formedbetween the outer metal thin-film wire and the inner metal thin-filmwire (see FIGS. 5(A), 7, 8, 9, and 10).

In a specific embodiment, the secondary coil (2) formed of the middlemetal thin-film wire between the outer metal thin-film wire and theinner metal thin-film wire is formed with a plural number of turns (seeFIGS. 5(A), 7, 8, and 10).

In a more specific embodiment, the first coil (1A), the secondary coil(2), and the second coil (1B) are formed of a multilayer wiringstructure formed over the surface of the substrate and, in themultilayer wiring structure, the secondary coil (2) is interposedbetween the first coil (1A) and the second coil (1B) (see FIG. 6).

In another specific embodiment, the substrate is a semiconductor chip(11), the first transistor (3A) and the second transistor (3B) areformed in the semiconductor chip (11), and the transformer is formed asan on-chip transformer on the semiconductor chip (11) (see FIGS. 11 and13).

In a further different specific embodiment, the substrate having thetransformer formed thereon is a wiring substrate (17), and the firsttransistor (3A) and the second transistor (3B) are formed in thesemiconductor chip (11) (see FIGS. 12 and 14).

The transformer formed on the wiring substrate (17) is electricallycoupled to each of the first transistor (3A) and the second transistor(3B) which are formed in the semiconductor chip (11) by a coupling wire.

In a still another specific embodiment, the primary coil (1A and 1B) ofthe transformer is formed in a symmetrical shape (see FIGS. 5(A) to 14).

According to the still another specific embodiment, even-numberedharmonic distortion in an amplified RF output signal generated from theoutput terminal (Output) of the secondary coil (2) can be reduced. As aresult, it is possible to reduce the problem of the deterioration of theadjacent channel leakage power ratio (ACPR) and the power addedefficiency (PAE).

In yet another specific embodiment, each of the first transistor (3A)and the second transistor (3B) is a MOS transistor (see FIGS. 5(A) to13, and 15).

Specifically, the MOS transistor is an LDMOS transistor.

In a still another specific embodiment, each of the first transistor(3A) and the second transistor (3B) is a bipolar transistor (see FIGS.14 and 17).

Specifically, the bipolar transistor is a compound semiconductorheterojunction bipolar transistor.

In a most specific embodiment, the one end and the other end of theprimary coil which are coupled to the first and second transistors andthe one end and the other end of the secondary coil from between whichthe output signal can be generated are formed at mutually opposinglocations in the annular shapes (see FIGS. 5(A) to 14).

2. An RF power amplifier according to a representative embodiment inanother aspect of the present invention includes a first transistor (3A)and a second transistor (3B) each as an active device of a push-pullpower amplification circuit, and a transformer (1A and 1B, and 2) as anoutput matching circuit of the push-pull power amplification circuit.

A non-inverted input signal (+Input) and an inverted input signal(−Input) can be supplied respectively to an input terminal of the firsttransistor (3A) and an input terminal of the second transistor (3B).

The transformer has a primary metal thin-film wire (1A and 1B) and asecondary metal thin-film wire (2), and the primary metal thin-film wireand the secondary metal thin-film wire are magnetically coupled to eachother, and have respective annular shapes each formed flat over asurface of a substrate.

One end (I1) of the primary metal thin-film wire (1A and 1B) of thetransformer is coupled to an output terminal of the first transistor(3A), while the other end (I2) of the primary metal thin-film wire ofthe transformer is coupled to an output terminal of the secondtransistor (3B).

An output signal (Output) can be generated from between one end (O1) andthe other end (O2) of the secondary metal thin-film wire (2) of thetransformer.

The one end (I1) and the other end (I2) of the primary metal thin-filmwire (1A and 1B) of the transformer and the one end (O1) and the otherend (O2) of the secondary metal thin-film wire (2) of the transformerare formed respectively in a first portion (B1) and a second portion(B2) of each of the annular shapes which oppose each other.

In the first portion (B1) of the annular shape, the one end (I1) and theother end (I2) of the primary metal thin-film wire (1A and 1B) of thetransformer are disposed proximate to each other.

In the second portion (B2) of the annular shape, the one end (O1) andthe other end (O2) of the secondary metal thin-film wire (2) of thetransformer are disposed proximate to each other.

The primary metal thin-film wire (1A and 1B) of the transformer includesat least a first wire (1A) and a second wire (1B) which are coupled inparallel between the output terminal of the first transistor (3A) andthe output terminal of the second transistor (3B), and each ismagnetically coupled to the secondary metal thin-film wire (2) (seeFIGS. 5(A) and 5(B)).

According to the embodiment described above, the primary metal thin-filmwire (1A and 1B) of the transformer includes at least the first wire(1A) and the second wire (1B) which are coupled in parallel. This allowsa reduction in the primary-side input impedance of the transformer.

Further, the one end (I1) and the other end (I2) of the primary metalthin-film wire (1A and 1B) of the transformer and the one end (O1) andthe other end (O2) of the secondary metal thin-film wire (2) of thetransformer are formed respectively in a first portion (B1) and a secondportion (B2) of each of the annular shapes which oppose each other. Inthe first portion (B1) of the annular shape, the one end (I1) and theother end (I2) of the primary metal thin-film wire (1A and 1B) aredisposed proximate to each other. In the second portion (B2) of theannular shape, the one end (O1) and the other end (O2) of the secondarymetal thin-film wire (2) are disposed proximate to each other. As aresult, the degree of coupling of the one end (O1) of the secondarymetal thin-film wire (2) functioning as the complementary outputterminal and one output of the transformer to the one end (I1) and theother end (I2) of the primary metal thin-film wire (1A and 1B)functioning as the complementary input terminals of the transformer canbe generally equalized to the degree of coupling of the other end (O2)of the secondary metal thin-film wire (2) functioning as thecomplementary output terminal and the other output of the transformer tothe one end (I1) and the other end (I2) of the primary metal thin-filmwire (1A and 1B). As a result, it is possible to improve the stabilityof the operation of the push-pull power amplification circuit of the RFpower amplifier.

Furthermore, according to the embodiment described above, the primarywire and secondary wire of the transformer are formed of respectivemetal thin-film wires (1A and 1B, and 2). This allows reductions in theheights of the members of the transformer, and allows a reduction in thesize of a mobile phone terminal when the RF power amplifier includingthe transformer is mounted in the mobile phone terminal.

In a preferred embodiment, at least one of the first wire (1A) and thesecond wire (1B) can be supplied with a power supply voltage (Vdd)between the output terminal of the first transistor (3A) and the outputterminal of the second transistor (3B) (see FIGS. 5(A) and 5(B)).

According to the preferred embodiment described above, it is notnecessary to use bonding wires as described in Non-Patent Document 4listed above when the power supply voltage (Vdd) is supplied to thefirst transistor (3A) and the second transistor (3B). The power supplyvoltage is supplied using the primary coil having a low impedance.Therefore, it is possible to reduce the problem of the deterioration ofthe power added efficiency due to signal loss in the bonding wiresdescribed in Non-Patent Document 4 listed above.

In a more preferred embodiment, the primary metal thin-film wire (1A and1B) of the transformer is formed to have a width larger than a width ofthe secondary metal thin-film wire (2) of the transformer.

In another preferred embodiment, the primary metal thin-film wire (1Aand 1B) of the transformer and the secondary metal thin-film wire (2) ofthe transformer are formed around the respective annular shapes.

The primary metal thin-film wire (1A and 1B) and the secondary metalthin-film wire (2) are set to a predetermined ratio of turns to allowthe transformer to execute an output matching operation in accordancewith an impedance transformation ratio determined by the ratio of turns.

In a still more preferred embodiment, the number of turns of thesecondary metal thin-film wire (2) is set to generally an integralmultiple of the number of turns of the primary metal thin-film wire (1Aand 1B).

In a yet more preferred embodiment, the first wire (1A) and the secondwire (1B) of the primary metal thin-film wire (1A and 1B) of thetransformer are formed respectively of an outer metal thin-film wire andan inner metal thin-film wire each having the annular shape.

The secondary metal thin-film wire (2) is formed of a middle metalthin-film wire formed between the outer metal thin-film wire and theinner metal thin-film wire (see FIGS. 5(A), 5(B), 7, 8, 9, and 10).

In a specific embodiment, the secondary metal thin-film wire (2) formedof the middle metal thin-film wire between the outer metal thin-filmwire and the inner metal thin-film wire is formed with a plural numberof turns (see FIGS. 5(A), 5(B), 7, 8, and 10).

In a more specific embodiment, the first wire (1A), the secondary metalthin-film wire (2), and the second wire (1B) are formed of a multilayerwiring structure formed over the surface of the substrate and, in themultilayer wiring structure, the secondary metal thin-film wire (2) isinterposed between the first wire (1A) and the second wire (1B) (SeeFIG. 6).

In another specific embodiment, the substrate is a semiconductor chip(11), the first transistor (3A) and the second transistor (3B) areformed in the semiconductor chip (11), and the transformer is formed asan on-chip transformer on the semiconductor chip (11) (see FIGS. 11 and13).

In a further different specific embodiment, the substrate having thetransformer formed thereon is a wiring substrate (17), and the firsttransistor (3A) and the second transistor (3B) are formed in thesemiconductor chip (11).

The transformer formed on the wiring substrate (17) is electricallycoupled to each of the first transistor (3A) and the second transistor(3B) which are formed in the semiconductor chip (11) by a coupling wire(see FIGS. 12 and 14).

In a still another specific embodiment, each of the first transistor(3A) and the second transistor (3B) is a MOS transistor (see FIGS. 5(A)and 5(B) to 13, and 15).

Specifically, the MOS transistor is an LDMOS transistor.

In a yet another specific embodiment, each of the first transistor (3A)and the second transistor (3B) is a bipolar transistor (see FIGS. 14 and17).

Specifically, the bipolar transistor is a compound semiconductorheterojunction bipolar transistor.

In a most specific embodiment, in the first portion (B1) of the annularshape, only the first transistor (3A) and the second transistor (3B) arecoupled to the one end (I1) and the other end (I2) of the primary metalthin-film wire (1A and 1B) of the transformer, each as the active devicecoupled to the primary metal thin-film wire.

The primary metal thin-film wire (1A and 1B) and the secondary metalthin-film wire (2) of the transformer are formed in respectivesymmetrical shapes with respect to an imaginary line coupling the firstportion (B1) and the second portion (B2) to each other (see FIGS. 5(A)and 5(B) to 14).

According to the most specific embodiment described above, the radiusand perimeter of the annular shape of the transformer have symmetricalshapes. This allows the elimination of a reduction in Q-factor. Inaddition, since even-numbered harmonic distortion in the amplified RFoutput signal generated from the output terminal (Output) of thesecondary metal thin-film wire (2) can be reduced, it is possible toreduce the problem of the deterioration of the adjacent channel leakagepower ratio (ACPR) and the power added efficiency (PAE).

Description of Embodiments

Next, the embodiments will be described in greater detail. Throughoutthe drawings for illustrating the best mode for carrying out theinvention, members having the same functions as in the drawingsdescribed above will be denoted by the same reference numerals, and arepeated description thereof is omitted.

<Basic Configuration of RF Power Amplifier>

FIGS. 5(A) to 5(D) are views each showing a basic configuration of an RFpower amplifier according to an embodiment of the present invention.

FIG. 5(A) shows a representative configuration in which a transformer isdisposed at a generally midpoint C1 between the input terminals I1 andI2 thereof and the output terminals O1 and O2 thereof. FIG. 5(B) shows aconfiguration in which the transformer is disposed at a position shiftedfrom the generally midpoint C1 between the input terminals I1 and I2thereof and the output terminals O1 and O2 thereof. FIG. 5(C) shows anenlarged view of the portion surrounded by the broken line B1 of FIG.5(A). FIG. 5(D) is a cross-sectional view of a portion along the lineA-A′ in FIG. 5(C). Note that the input terminals I1 and I2 and theoutput terminals O1 and O2 of the transformer are respectively formed inthe above-mentioned first and second portions B1 and B2 of each of theannular shapes which oppose each other.

That is, in the RF power amplifier shown in FIGS. 5(A) to 5(D), twosource-grounded high-breakdown-voltage N-channel MOS transistors 3A and3B are used as active devices. The respective input terminals, outputterminals, and ground terminals of the transistors serve as therespective gates, drains, and sources thereof. As an output matchingcircuit and a power combining circuit, an on-chip transformer is usedwhich includes a plurality of (two) metal wires 1A and 1B as a primarycoil having an annular shape, and a metal thin-film wire 2 as a 3-turnmetal strip of a secondary coil between the two metal wires 1A and 1B ofthe primary coil. Between the respective drains of the N-channel MOStransistors 3A and 3B of one push-pull power amplification circuit, thetwo outer and inner metal wires 1A and 1B as the primary coil of theon-chip transformer are coupled in parallel. Since the parallel couplingthereof reduces the inductance of the primary coil, it is possible toreduce the input impedance of the primary coil of the on-chiptransformer. In addition, since the widths of the two thin-film metalwires 1A and 1B of the primary coil are set larger than the width of themetal thin-film wire 2 of the secondary coil, it is possible to reducethe input impedance of the primary coil of the on-chip transformer. Atthis time, since the radius and perimeter of the annular shape of thetransformer can be held without being reduced, it is possible toeliminate a reduction in Q-factor.

At the middle of the uppermost side of the annular shape, the powersupply voltage Vdd is supplied to the midpoint of the outer metal wire1A as the primary coil. At the middle of the uppermost side of theannular shape, the power supply voltage Vdd can be supplied to themidpoint of the inner metal wire 1B as the primary coil via a cross wireor the like not shown, though not depicted in FIGS. 5(A) to 5(D).Therefore, it is possible to reduce the problem of the deterioration ofthe power added efficiency due to signal loss in the bonding wires forsupplying the power supply voltage to the respective drains of theN-channel MOS transistors, which has been described with reference toFIG. 4.

As shown in FIGS. 5(A) and 5(C), the drain of the N-channel MOStransistor 3A as one of the N-channel MOS transistors is coupled to oneend (first input terminal I1) of the outer metal wire 1A and to one endof a lower-layer cross wire 5A at locations leftward of the middle ofthe lowermost side of the annular shape, while the other end of thelower-layer cross wire 5A is coupled to one end of the inner metal wire1B. The drain of the N-channel MOS transistor 3B as the other of theN-channel MOS transistors is coupled to the other end (second inputterminal I2) of the outer metal wire 1A and to one end of a lower-layercross wire 5B at locations rightward of the middle of the lowermost sideof the annular shape, while the other end of the lower-layer cross wire5B is coupled to the other end of the inner metal wire 1B. Note that, asshown in FIG. 5(D), the metal wires 1A and 1B as the primary coil of thetransformer, the secondary coil 2 of the transformer, and thelower-layer cross wires 5A and 5B are formed of a multilayer wiringstructure. Over the surface of a substrate Sub, a first-layer insulatingfilm Ins1 is formed. Over the surface of the first-layer insulating filmIns1, the lower-layer cross wire 5B and a second-layer insulating filmIns2 are formed. Over the surface of the second-layer insulating filmIns2, the metal wires 1A and 1B as the primary coil of the transformerand the secondary coil 2 of the transformer are formed. Over the metalwires 1A and 1B and the secondary coil 2, a third-layer insulating filmIns3 is formed. The two outer and inner metal wires 1A and 1B as theprimary coil are coupled in parallel, and the primary coil is formedwith one turn around the annular shape.

To the gate of the N-channel MOS transistor 3A as one of the N-channelMOS transistors, the non-inverted input signal +Input is supplied, whilethe inverted input signal −Input is supplied to the gate of theN-channel MOS transistor 3B as the other of the N-channel MOStransistors. The length of each of the metal wires 1A and 1B of theprimary coil is generally equal to the perimeter of the annular shape,and the parallel coupling of the two metal wires 1A and 1B of theprimary coil allows the input impedance of the primary coil between therespective drains of the two N-channel MOS transistors 3A and 3B to bereduced to one-half. Note that, between the respective drains of the twoN-channel MOS transistors 3A and 3B, a capacitor 4 for reducing thelevel of an odd-numbered harmonic is coupled. The capacitor 4 is formedof, e.g., a MIM capacitor that can be manufactured by a CMOSmanufacturing process. The MIM capacitor is formed by forming capacitiveelectrodes over and under a capacitive insulating film. Note that MIM isthe abbreviation of Metal-Insulator-Metal.

Between the two metal wires 1A and 1B coupled in parallel of the primarycoil, the metal thin-film wire 2 as the metal strip of the secondarycoil is disposed with three turns. One end (second output terminal O2)of the metal thin-film wire 2 which is located rightward of the middleof the uppermost side of the annular shape is coupled to a groundvoltage GND via a lower-layer cross wire 5D. The metal thin-film wire 2is formed to extend from a start point corresponding to the one endthereof located rightward of the middle of the uppermost side of theannular shape, make three clockwise turns, and reach an end pointcorresponding to the other end (first output terminal O1) thereoflocated leftward of the middle of the uppermost side of the annularshape. The end point corresponding to the other end located leftward ofthe middle of the uppermost side of the annular shape is coupled to alower-layer cross wire 5C, and the output signal Output is generated viathe lower-layer cross wire 5C. Accordingly, the ratio of turns (TurnRatio) between the primary coil and the secondary coil is 1:3 so thatthe impedance transformation ratio in the basic theory of the on-chiptransformer as the output impedance matching circuit of the RF poweramplifier is 1:3². The present inventors have calculated the impedancetransformation ratio of the RF power amplifier shown in FIGS. 5(A) to5(D) by electromagnetic field simulation, and found that an impedancetransformation ratio of 1:11, which is more excellent than the value inthe basic theory, is obtainable. The reason that the impedancetransformation ratio more excellent than the value in the basic theoryis obtainable with the RF power amplifier shown in FIGS. 5(A) to 5(D)results from the reduction of the input impedance of the primary coilformed of the two parallel-coupled metal wires 1A and 1B to one-half ofan input impedance obtained in a normal case.

In the RF power amplifier shown in FIGS. 5(A) to 5(D), it is suggestedto use a high-breakdown-voltage transistor having a relatively highoutput impedance as each of the N-channel MOS transistors 3A and 3B ofthe push-pull power amplification circuit. As the high-breakdown-voltagetransistor, there can be used a laterally diffused (LD) N-channel MOStransistor or a high-breakdown-voltage npn-type heterojunction bipolartransistor using a compound semiconductor such as GaAs.

In contrast to the DAT power amplifier shown in FIG. 1, in the RF poweramplifier shown in FIGS. 5(A) to 5(D), the two metal wires 1A and 1B ofthe primary coil are coupled in parallel. Since the number of thepush-pull power amplification circuits arranged around the annular shapeis reduced to one-fourth, the input impedance of the primary coil isgenerally doubled. Therefore, by using a high-breakdown-voltagetransistor having a relatively high output impedance as each of theN-channel MOS transistors 3A and 3B of the RF power amplifier shown inFIGS. 5(A) to 5(D), it is possible to obtain impedance matchingconditions between the output impedance of the MOS transistors and theinput impedance of the primary coil of the transformer.

In the LD N-channel MOS transistor, an N-type low-impurity-concentrationregion is formed between the gate and the drain, thereby significantlyimproving the breakdown voltage thereof compared with that of a typicalshort-channel MOS transistor formed by a normal CMOS manufacturingprocess. Because the low-impurity-concentration region of the LDN-channel MOS transistor reduces the drain output capacitance thereof, ahigh-efficiency and low-distortion-factor RF power amplificationcharacteristic is obtainable. Because of the high breakdown voltage,resistance to dielectric breakdown can also be improved.

By using an LD N-channel MOS transistor as each of the N-channel MOStransistors 3A and 3B of the RF power amplifier shown in FIGS. 5(A) to5(D), it is possible to obtain excellent impedance matching conditionsbetween the relatively high output impedance of the LDMOS transistorsand the input impedance of the primary coil of the transformer.

In the power amplifier shown in FIG. 4 also, the number of the push-pullpower amplification circuits arranged around the annular shape isreduced to one-fourth of that in the DAT power amplifier shown inFIG. 1. Accordingly, the input impedance of the primary coil isgenerally quadrupled. Even when an LDMOS transistor having a relativelyhigh output impedance is used as each of the N-channel MOS transistors7A, 7B, 7C, and 7D of the RF power amplifier of FIG. 4, it has beenimpossible to obtain excellent impedance matching conditions between theMOS transistors and the input impedance of the primary coil of thetransformer. As a result, it has been recognized by the presentinventors that the maximum RF output power Pout(max) when the LDMOStransistor is employed in the power amplifier shown in FIG. 4 isgenerally 33 dBm at most.

By contrast, when the LDMOS transistor is employed in the RF poweramplifier shown in FIGS. 5(A) to 5(D), excellent impedance matchingconditions can be obtained. As a result, it has been recognized by thepresent inventors that the maximum RF output power Pout(max) can beincreased to generally 35 dBm.

In the RF power amplifier shown in FIGS. 5(A) to 5(D), the radius andperimeter of each of the annular shapes of the two metal wires 1A and 1Bof the primary coil of the on-chip transformer are bilaterallysymmetrical relative to the annular shape. Therefore, even-numberedharmonic distortion in the amplified RF output signal generated from theoutput terminal Output of the secondary coil 2 can be reduced, andtherefore the problem of the deterioration of the adjacent channelleakage power ratio (ACPR) and the power added efficiency (PAE) can bereduced.

<Another Configuration of RF Power Amplifier>

FIG. 6 is a view showing another configuration of the RF power amplifieraccording to the embodiment of the present invention.

That is, the RF power amplifier shown in FIG. 6 is different from the RFpower amplifier shown in FIG. 5 (5(A) to 5(D)) in the following point.

In the RF power amplifier shown in FIG. 6, the two metal wires 1A and 1Bcoupled in parallel of the primary coil are formed over and under themetal thin-film wire 2 disposed with two turns as the metal strip of thesecondary coil, as shown in the right-hand cross-sectional structure ofFIG. 6. As a result, the metal wire 1B, the metal thin-film wire 2, andthe metal wire 1A are formed respectively of the first-layer metal wire,the second-layer metal wire, and the third-layer metal wire eachoverlying a Si chip.

As shown in the plan view of FIG. 6, one end of the metal thin-film wire2 as the second-layer metal wire which is located rightward of themiddle of the uppermost side of the annular shape thereof is coupled tothe ground voltage GND via the lower-layer cross wire 5D. The metalthin-film wire 2 is formed to extend from a start point corresponding tothe inner one end thereof located rightward of the middle of theuppermost side of the annular shape, make two clockwise turns, and reachan end point corresponding to the outer other end thereof locatedleftward of the middle of the uppermost side of the annular shape.Between the outer other end of the metal thin-film wire 2 which islocated leftward of the middle of the uppermost side of the annularshape thereof and the inner one end of the metal thin-film wire 2 whichis located rightward of the middle of the uppermost side of the annularshape thereof, the inner annular shape portion of the metal thin-filmwire 2 and the outer annular shape portion thereof are coupled. Also,between the outer other end of the metal thin-film wire 2 and the innerone end thereof, the power supply voltage Vdd is supplied to themidpoint of the metal wire 1B as the first-layer metal wire and to themidpoint of the metal wire 1A as the third-layer metal wire.

In the RF power amplifier shown in FIG. 6 also, the two outer and innermetal wires 1A and 1B as the primary coil of the on-chip transformer arecoupled in parallel between the respective drains of the N-channel MOStransistors 3A and 3B of the one push-pull power amplification circuit.The parallel coupling thereof reduces the inductance of the primarycoil, and can reduce the input impedance of the primary coil. At thistime, the radius and perimeter of the annular shape of the transformercan be held without being reduced and hence a reduction in Q-factor canbe eliminated.

Further, at the middle of the uppermost side of the annular shape, thepower supply voltage Vdd is supplied to the midpoint of the metal wire1B as the first-layer metal wire and to the midpoint of the metal wire1A as the third-layer metal wire. Therefore, it is possible to reducethe problem of the deterioration of the power added efficiency due tosignal loss in the bonding wires for supplying the power supply voltageto the respective drains of the N-channel MOS transistors, which hasbeen described with reference to FIG. 4.

In the RF power amplifier shown in FIG. 6, the ratio of turns (TurnRatio) between the primary coil and the secondary coil is 1:2 so thatthe impedance transformation ratio in the basic theory of the on-chiptransformer as the output impedance matching circuit of the RF poweramplifier is 1:2². The present inventors have calculated the impedancetransformation ratio of the RF power amplifier shown in FIG. 6 byelectromagnetic field simulation, and found that an impedancetransformation ratio of 1:5.7, which is more excellent than the value inthe basic theory, is obtainable. The reason that the impedancetransformation ratio more excellent than the value in the basic theoryis obtainable with the RF power amplifier shown in FIG. 6 results fromthe reduction of the input impedance of the primary coil formed of thetwo parallel-coupled metal wires 1A and 1B to one-half of an inputimpedance obtained in a normal case.

By using an LD N-channel MOs transistor as each of the N-channel MOStransistors 3A and 3B of the RF power amplifier shown in FIG. 6,excellent impedance matching conditions can be obtained between therelatively high output impedance of the LDMOS transistors and the inputimpedance of the primary coil of the transformer.

In the RF power amplifier shown in FIG. 6 also, the radius and perimeterof each of the annular shapes of the two metal wires 1A and 1B of theprimary coil of the on-chip transformer are bilaterally symmetricalrelative to the annular shape. Therefore, it is possible to reduceeven-numbered harmonic distortion in the amplified RF output signalgenerated from the output terminal Output of the secondary coil 2, andreduce the deterioration of the adjacent channel leakage power ratio(ACPR) and the power added efficiency (PAE). Note that, in FIG. 6, thetwo metal wires 1A and 1B of the primary coil which are formed over andunder the metal thin-film wire 2 of the secondary coil are electricallycoupled to each other by vias 6A and 6B. Through holes are formed in theinterlayer insulating film between the metal wires 1A and 1B formed overand under the metal thin-film wire 2, and the vias 6A and 6B are formedby filling the through holes with a wiring metal.

FIG. 7 is a view showing still another configuration of the RF poweramplifier according to the embodiment of the present invention.

That is, the RF power amplifier shown in FIG. 7 is different from the RFpower amplifier shown in FIG. 5 in the following point.

In the RF power amplifier shown in FIG. 7, the metal thin-film wire 2disposed with two turns as the metal strip of the second coil is formedbetween three metal wires 1A, 1B, and 1C coupled in parallel of theprimary coil.

As shown in the plan view of FIG. 7, one end of the metal thin-film wire2 which is located rightward of the middle of the uppermost side of theannular shape thereof is coupled to the ground voltage GND via thelower-layer cross wire 5D. The metal thin-film wire 2 is formed toextend from a start point corresponding to the inner one end thereoflocated rightward of the middle of the uppermost side of the annularshape, make two clockwise turns, and reach an end point corresponding tothe outer other end thereof located leftward of the middle of theuppermost side of the annular shape. Between the outer other end of themetal thin-film wire 2 which is located leftward of the middle of theuppermost side of the annular shape thereof and the inner one end of themetal thin-film wire 2 which is located rightward of the middle of theuppermost side of the annular shape thereof, the inner annular shapeportion of the metal thin-film wire 2 and the outer annular shapeportion thereof are coupled. Also, between the outer other end of themetal thin-film wire 2 and the inner one end thereof, the power supplyvoltage Vdd is supplied to the midpoint of the metal wire 1C, to themidpoint of the metal wire 1B, and to the midpoint of the metal wire 1A.

In the RF power amplifier shown in FIG. 7 also, the three outer, middle,and inner metal wires 1A, 1B, and 1C are coupled in parallel as theprimary coil of the on-chip transformer between the respective drains ofthe N-channel MOS transistors 3A and 3B of the one push-pull poweramplification circuit. The parallel coupling thereof reduces theinductance of the primary coil, and can reduce the input impedance ofthe primary coil. In addition, since the width of each of the threemetal wires 1A, 1B, and 1C of the primary coil is set larger than thewidth of the metal thin-film wire 2 of the secondary coil, it ispossible to reduce the input impedance of the primary coil of theon-chip transformer. It has been recognized by the present inventorsthat, compared with the maximum RF output power Pout(max) in each of theRF power amplifiers shown in FIGS. 5 and 6, the maximum RF output powerPout(max) in the RF power amplifier shown in FIG. 7 increases generallyby 0.5 dBm. Moreover, since the radius and perimeter of the annularshape of the transformer can be held without being reduced, a reductionin Q factor can be eliminated.

Furthermore, since the power supply voltage Vdd is supplied to themidpoint of the inner metal wire 1C, to the midpoint of the middle metalwire 1B, and to the midpoint of the outer metal wire 1A, it is possibleto reduce the problem of the deterioration of the power added efficiencydue to signal loss in the bonding wires for supplying the power supplyvoltage to the respective drains of the N-channel MOS transistors, whichhas been described with reference to FIG. 4.

In the RF power amplifier shown in FIG. 7 also, the ratio of turns (TurnRatio) between the primary coil and the secondary coil is 1:2 so thatthe impedance transformation ratio in the basic theory of the on-chiptransformer as the output impedance matching circuit of the RF poweramplifier is 1:2². The present inventors have calculated the impedancetransformation ratio of the RF power amplifier shown in FIG. 7 byelectromagnetic field simulation, and found that an impedancetransformation ratio of 1:6, which is more excellent than the value inthe basic theory, is obtainable. The reason that the impedancetransformation ratio more excellent than the value in the basic theoryis obtainable with the RF power amplifier shown in FIG. 7 results fromthe reduction of the input impedance of the primary coil formed of thethree parallel-coupled metal wires 1A, 1B, and 1C to one-third of aninput impedance obtained in a normal case.

By using an LD N-channel MOS transistor as each of the N-channel MOStransistors 3A and 3B of the RF power amplifier shown in FIG. 7,excellent impedance matching conditions can be obtained between therelatively high output impedance of the LDMOS transistors and the inputimpedance of the primary coil of the transformer.

In the RF power amplifier shown in FIG. 7 also, the radius and perimeterof each of the annular shapes of the three metal wires 1A, 1B, and 1C ofthe primary coil of the on-chip transformer are bilaterally symmetrical.Therefore, it is possible to reduce even-numbered harmonic distortion inthe amplified RF output signal generated from the output terminal Outputof the secondary coil 2, and reduce the deterioration of the adjacentchannel leakage power ratio (ACPR) and the power added efficiency (PAE).

FIG. 8 is a view showing yet another configuration of the RF poweramplifier according to the embodiment of the present invention.

That is, the RF power amplifier shown in FIG. 8 is different from the RFpower amplifier shown in FIG. 7 in the following point.

In the RF power amplifier shown in FIG. 8, the metal thin-film wire 2 asthe metal strip of the secondary coil has one more additional turnbetween the outer metal wire 1A and the middle metal wire 1B of theprimary coil of the transformer. Accordingly, the number of turns of themetal thin-film wire 2 is three so that the ratio of turns (Turn Ratio)between the primary coil and the secondary coil is 1:3, and theimpedance transformation ratio in the basic theory of the on-chiptransformer as the output impedance matching circuit of the RF poweramplifier is 1:3². In the RF power amplifier shown in FIG. 8 also,generally the same useful operation and effect as achieved with each ofthe RF power amplifiers according to the various embodiments of thepresent invention shown in FIGS. 5 to 7 can be achieved.

FIG. 9 is a view showing still another configuration of the RF poweramplifier according to the embodiment of the present invention.

That is, the RF power amplifier shown in FIG. 9 is different from the RFpower amplifier shown in FIG. 5 in the following point.

In the RF power amplifier shown in FIG. 9, the metal thin-film wire 2 asthe metal strip of the secondary coil has one turn, instead of threeturns, between the outer metal wire 1A and the inner metal wire 1B ofthe primary coil of the transformer. Accordingly, the number of turns ofthe metal thin-film wire 2 is one so that the ratio of turns (TurnRatio) between the primary coil and the secondary coil is 1:1, and theimpedance transformation ratio in the basic theory of the on-chiptransformer as the output impedance matching circuit of the RF poweramplifier is 1:1². However, between the respective drains of theN-channel MOS transistors 3A and 3B of the one push-pull poweramplification circuit, the two outer and inner metal wires 1A and 1B ofthe primary coil are coupled in parallel. As a result, the inductance ofthe primary coil is reduced to allow a reduction in the input impedanceof the primary coil of the on-chip transformer. The present inventorshave calculated the impedance transformation ratio of the RF poweramplifier of FIG. 9 by electromagnetic field simulation, and found thatan impedance transformation ratio of 1:2.1, which is more excellent thanthe value in the basic theory, is obtainable. The reason for this alsoresults from the reduction of the input impedance of the primary coilformed of the two parallel-coupled metal wires 1A and 1B to one-half ofan input impedance obtained in a normal case. In the RF power amplifiershown in FIG. 9 also, generally the same useful operation and effect asachieved with each of the RF power amplifiers according to the variousembodiments of the present invention shown in FIGS. 5 to 7 can beachieved.

FIG. 10 is a view showing yet another configuration of the RF poweramplifier according to the embodiment of the present invention.

That is, the RF power amplifier shown in FIG. 10 is different from theRF power amplifier shown in FIG. 9 in the following point.

In the RF power amplifier shown in FIG. 10, the metal thin-film wire 2as the metal strip of the secondary coil has two turns, instead of oneturn, between the outer metal wire 1A and the inner metal wire 1B of theprimary coil of the transformer. Accordingly, the number of turns of themetal thin-film wire 2 is two so that the ratio of turns (Turn Ratio)between the primary coil and the secondary coil is 1:2, and theimpedance transformation ratio in the basic theory of the on-chiptransformer as the output impedance matching circuit of the RF poweramplifier is 1:2². However, between the respective drains of theN-channel MOS transistors 3A and 3B of the one push-pull poweramplification circuit, the two outer and inner metal wires 1A and 1B ofthe primary coil are coupled in parallel. As a result, the inductance ofthe primary coil is reduced to allow a reduction in the input impedanceof the primary coil of the on-chip transformer. The present inventorshave calculated the impedance transformation ratio of the RF poweramplifier of FIG. 10 by electromagnetic field simulation, and found thatan impedance transformation ratio of 1:5.7, which is more excellent thanthe value in the basic theory, is obtainable. The reason for this alsoresults from the reduction of the input impedance of the primary coilformed of the two parallel-coupled metal wires 1A and 1B to one-half ofan input impedance obtained in a normal case. In the RF power amplifiershown in FIG. 10 also, generally the same useful operation and effect asachieved with each of the RF power amplifiers according to the variousembodiments of the present invention shown in FIGS. 5 to 7 can beachieved.

<Monolithic RF Power Amplifier>

FIG. 11 is a view showing a configuration of a monolithic RF poweramplifier according to another embodiment of the present invention inwhich the transformer and the N-channel MOS transistors of the onepush-pull power amplification circuit, each illustrated in FIG. 5, areintegrated in a Si chip.

That is, in the monolithic RF power amplifier shown in FIG. 11, thetransformer 11 for output impedance matching and the differential pair 3of the MOS transistors 3A and 3B, each illustrated in FIG. 5, and atransformer 12 for input impedance matching are integrated in a Si chip10. The Si chip 10 has been pellet-bonded onto a rectangular tab, and aplurality of external leads 13 to 16 have been formed around therectangular tab. The plurality of external leads 13 to 16 and aplurality of bonding pads of the Si chip 10 are electrically coupled toeach other by a plurality of bonding wires.

A differential pair of input signals supplied from the two externalleads 16 are supplied to the respective gates of each of the pairs ofMOS transistors in the differential pair 3 via the input impedancematching transformer 12, and a differential pair of output signals fromthe respective drains of the pair of MOS transistors in the differentialpair 3 are supplied to the primary coil of the output impedance matchingtransformer 11. RF transmission differential output signals generatedfrom the secondary coil of the output impedance matching transformer 11can be supplied to an antenna mounted in a mobile phone terminal via thetwo external leads 13 and 14. In addition, the power supply voltage Vddsupplied via the external lead 15 disposed between the two externalleads 13 and 14 can also be supplied to each of the respective midpointsof the outer and inner metal wires of the primary coil having theannular shape of the output impedance matching transformer 11. Theexternal lead 15 disposed between the two external leads 13 and 14 hasthe function of reducing undesired crosstalk between the two externalleads 13 and 14.

The transformers and the N-channel MOS transistors of the push-pullpower amplification circuit which are integrated in the Si chip 10 ofthe monolithic RF power amplifier shown in FIG. 11 are not limited tothe structures shown in FIG. 5. Any of the structures shown in FIGS. 6to 10 can be integrated as the transformers and the N-channel MOStransistors of the push-pull power amplification circuit which areintegrated in the Si chip 10 of the monolithic RF power amplifier shownin FIG. 11. Note that, over the surface of the Si chip 10 of themonolithic RF power amplifier shown in FIG. 11, a resin for providingmechanical and electrical protection and the prevention of the entranceof moisture has been formed.

<RF Power Amplifier Module>

FIG. 12 is a view showing a configuration of an RF power amplifiermodule according to still another embodiment of the present invention,in which the Si chip 10 having integrated therein the N-channel MOStransistors of the one push-pull power amplification circuit, and theoutput impedance matching transformer 11 illustrated in FIG. 9 areembedded.

That is, in the RF power amplifier module shown in FIG. 12, thedifferential pair 3 of the MOS transistors 3A and 3B and the transformer12 for the input impedance matching have been integrated in the Si chip10. In addition, over a printed substrate 17 of the RF power amplifiermodule, the Si chip 10, the transformer 11 for the output impedancematching illustrated in FIG. 9, chip capacitors 18A and 18B, and a metalthin-film inductor 19 have been formed.

In the case of forming a metal thin-film wire over the printed substrate17, the formation of a minute pattern is more difficult than in the caseof forming the metal thin-film wire over the Si chip 10. That is, in thecase of forming the output impedance matching transformer 11 over theprinted substrate 17, it is difficult to implement the secondary coilswith two or more turns. Therefore, in the RF power amplifier moduleshown in FIG. 12, there is employed the on-chip transformer 11 as theoutput impedance matching circuit in which the secondary coil shown inFIG. 9 has one turn, and the ratio of turns between the primary coil andthe secondary coil is 1:1. As a result, however, the on-chip transformer11 has a slightly insufficient impedance transformation ratio so that anauxiliary output impedance matching circuit formed of passive elementswhich are the chip capacitor 18A and the metal thin-film inductor 19 iscoupled to the output of the transformer 11. The auxiliary outputimpedance matching circuit functions also as a lowpass filter whichreduces an unneeded harmonic component. Note that the chip capacitor 18Bis for reducing the level of an odd-numbered harmonic in the push-pullpower amplification circuit. Over the surface of the RF power amplifiermodule of FIG. 12, a resin for providing mechanical and electricalprotection and the prevention of the entrance of moisture has beenformed. A transformer which is mounted over the printed substrate 17 ofthe RF power amplifier module of FIG. 12 is not limited to the structureshown in FIG. 9. Any of the structures shown in FIGS. 5 to 8 and 10 canbe mounted over the printed substrate 17 of the RF power amplifiermodule of FIG. 12. Note that, in FIG. 12, a plurality of vias 20, 21,22A, and 22B are formed over the printed substrate 17, and the viascouple the upper layer wiring and lower layer wiring of the multilayerwiring to each other inside the printed substrate 17. The via 20 is usedto obtain an output signal from the auxiliary output impedance matchingcircuit formed of the chip capacitor 18A and the metal thin-filminductor 19. The via 21 is used to supply the power supply voltage tothe primary coil of the transformer 11. The vias 22A and 22B are used tocouple one terminal of each of the chip capacitors 18A and 18B to aground electrode at the back surface of the printed substrate 17.

FIG. 13 is a view showing a configuration of the RF power amplifiermodule according to yet another embodiment of the present inventionhaving embedded therein the Si chip 10 in which the N-channel MOStransistors of the one push-pull power amplification circuit and theoutput impedance matching transformer 11 described in FIG. 9 areintegrated.

The RF power amplifier module shown in FIG. 13 is different from the RFpower amplifier module shown in FIG. 12 in the following point.

That is, in the RF power amplifier module shown in FIG. 13, thedifferential pair 3 of the MOS transistors 3A and 3B, the inputimpedance matching transformer 12, the output impedance matchingtransformer 11 illustrated in FIG. 9, and MIM capacitors 18C and 18D areintegrated in the Si chip 10. Further, over the printed substrate 17 ofthe RF power amplifier module, the Si chip 10 and the metal thin-filminductor 19 are formed. The metal thin-film inductor 19 over the printedsubstrate 17 and the MIM capacitor 18C over the Si chip 10 cooperatewith the auxiliary output impedance matching circuit to function as alowpass filter which reduces an unneeded harmonic component. Note thatthe MIM capacitor 18D is for reducing the level of an odd-numberedharmonic in the push-pull power amplification circuit. Over the surfaceof the RF power amplifier module of FIG. 13, a resin for providingmechanical and electrical protection and the prevention of the entranceof moisture has been formed. A transformer which is integrated in the Sichip 10 mounted over the printed substrate 17 of the RF power amplifiermodule of FIG. 13 is not limited to the structure shown in FIG. 9. Anyof the structures shown in FIGS. 5 to 8 and 10 can be integrated in theSi chip 10 mounted over the printed substrate 17 of the RF poweramplifier module of FIG. 13.

FIG. 14 is a view showing a configuration of the RF power amplifiermodule according to still another embodiment of the present inventionhaving embedded therein a GaAs chip 41 in which a high-breakdown-voltagenpn-type heterojunction bipolar transistor (HBT) 40 is integrated aseach of the transistors of the push-pull power amplification circuit,and the output impedance matching transformer 11 illustrated in FIG. 9.

The RF power amplifier module shown in FIG. 14 is different from the RFpower amplifier module shown in FIG. 12 in that the Si chip 10 of FIG.12 in which the N-channel MOS transistors are integrated has beenreplaced with the GaAs compound semiconductor semi-insulating chip 41 inwhich the HBT 40 is integrated, and otherwise identical thereto.

<LDMOS Transistor>

FIG. 15 is a view showing a configuration of an LDMOS transistor used inthe push-pull power amplification circuit of any of the RF poweramplifiers according to the various embodiments of the present inventionshown in FIGS. 5 to 13.

In the upper plan view of FIG. 15, two LDMOS transistors and a MIMcapacitor between the respective drain electrodes D thereof are shown.The MIM capacitor reduces the level of an odd-numbered harmonic. To therespective gate electrodes G of the two LDMOS transistors, adifferential pair of input signals are supplied. To the common sourceelectrode S of the two LDMOS transistors, a ground voltage is supplied.Note that the two LDMOS transistors have a finger electrode structure inwhich the plurality of source electrodes S and the plurality of drainelectrodes D are interdigitated with each other.

In the lower cross-sectional view of FIG. 15, a cross-sectionalstructure of a part of the LDMOS transistor located on the right-handside of the upper plan view of FIG. 15 is shown.

Each of the two LDMOS transistors includes, e.g., a P⁻-type(low-impurity-concentration) Si substrate 23, a P-type well 24, a Sioxide film 25, a polycrystalline Si film (gate electrode) 26, an N-typeSi layer (low-impurity-concentration source diffusion layer) 40, anN⁻-type Si layer (low-impurity-concentration drain diffusion layer) 28,an N⁺-type Si layer (high-impurity-concentration drain diffusion layer)29, an N⁺-type Si layer (high-impurity-concentration source diffusionlayer) 30, a P⁺-type Si layer 31, metal films 32 to 35, and aninsulating film 36. The drain 28 and source 31 of each of the LDMOStransistors are symmetrically formed with respect to the gate 26.

In the LDMOS transistor shown in the lower cross-sectional view of FIG.15, the low-impurity-concentration drain diffusion layer 28 and anoffset drain structure ODS are formed between the gate electrode 26 andthe high-impurity-concentration drain diffusion layer 29. The Sisubstrate (p-type Si substrate 23) is assumed to have a low impurityconcentration, and a high resistivity. Accordingly, the LDMOS transistorshown in FIG. 15 is assumed to have a breakdown voltage higher than thatof a short-channel MOS transistor formed by a CMOS manufacturingprocess. In addition, because the drain output capacitance of the LDMOStransistor is reduced, and the channel resistance of a source-draincurrent path has a relatively large value, the output impedance also hasa relatively large value.

The LDMOS transistor shown in the lower cross-sectional view of FIG. 15is different from a typical LDMOS transistor in that the Si substrate 23has a low impurity concentration, and a high resistivity.

FIG. 16 is a view showing a structure of a typical LDMOS transistor fora comparison with the LDMOS transistor shown in the lowercross-sectional view of FIG. 15.

In the LDMOS transistor having a typical structure shown in FIG. 16, theP⁻-type (low-impurity-concentration) Si substrate 23 of FIG. 15 has beenreplaced with a P⁻-type (low-impurity-concentration) Si layer 38 of FIG.16, and a P⁺-type Si substrate 37 is formed under the P⁻-type Si layer38. Additionally, in the LDMOS transistor having the typical structureshown in FIG. 16, the source electrode is electrically coupled to theP⁺-type polycrystalline Si layer 39 that has been formed deep so as toextend through the P⁻-type Si layer 38, and reach the P⁺-type Sisubstrate 37. The LDMOS transistor having the typical structure shown inFIG. 16 is mounted in an RF power amplifier module, and the P⁺-type Sisubstrate 37 is coupled to the ground electrode of the RF poweramplifier module which also has the function of a heat radiator plate.The ground electrode of the RF power amplifier module which also has thefunction of the heat radiator plate is coupled to the ground wire of thecircuit substrate of a mobile phone terminal. As a result, when theLDMOS transistor having the typical structure shown in FIG. 16 is usedas a source-grounded power transistor in the final amplification stageof the RF power amplifier module, fluctuations in the ground voltage ofthe source electrode in which a source current having a large valueflows are reduced, and heat radiation from the RF power amplifier modulecan be improved.

By contrast, in the push-pull power amplification circuit of any of theRF power amplifiers according to the various embodiments of the presentinvention shown in FIGS. 5 to 13 in which the LDMOS transistor shown inthe lower cross-sectional view of FIG. 15 is used, the two LDMOStransistors shown in FIG. 15 perform differential operations. As aresult, an alternating current flowing in the common source of the twoLDMOS transistors are mutually cancelled out so that the alternatingcurrent flowing into or out of the common source of the two LDMOStransistors becomes zero. Therefore, in the RF power amplifier module inwhich the two LDMOS transistors shown in FIG. 15 are mounted as thesource-grounded power transistors in the final amplification stage,sufficient grounding is achieved merely by coupling the common source ofthe two LDMOS transistors to the grounding wire of the circuit substrateof a mobile phone terminal via, e.g., an external lead. This is becausethe alternating current flowing into or out of the common source of thetwo LDMOS transistors becomes zero, and a current flowing in theexternal lead becomes zero. However, in that case, it is suggested tocouple the P⁻-type (low-impurity-concentration) Si substrate 23 formedwith the LDMOS transistor shown in FIG. 15 to the heat radiator plate ofthe RF power amplifier module, and thereby improve heat radiation fromthe RF power amplifier module.

In addition, since the P⁻-type Si substrate 23 formed with the LDMOStransistor shown in FIG. 15 has a low impurity concentration, and a highresistivity, it is possible to reduce power loss when the on-chiptransformer in which the two LDMOS transistors are coupled to theP⁻-type Si substrate 23 is formed. For example, a case is assumed wherean on-chip transformer having any of the structures of FIGS. 5 to 10 isformed in the P⁻-type Si substrate 23 shown in FIG. 15. Under theinfluence of a magnetic field at the center of the annular shape of theon-chip transformer, an eddy current may flow around the magnetic fieldat the center. In the LDMOS transistor shown in FIG. 15, the P⁻-type Sisubstrate 23 has a low impurity concentration, and a high resistivity sothat the value of the eddy current is small, and power loss due to theeddy current is small. However, in the LDMOS transistor having thetypical structure shown in FIG. 16, the P⁺-type Si substrate 37 has ahigh impurity concentration, and a low resistivity so that the value ofthe eddy current is large, and power loss due to the eddy current isalso large.

<High-Breakdown-Voltage Heterojunction Bipolar Transistor>

FIG. 17 is a view showing a configuration of a high-breakdown-voltagenpn-type heterojunction bipolar transistor (HBT) used in the push-pullpower amplification circuit of the RF power amplifier according to thestill another embodiment of the present invention shown in FIG. 14.

In the upper plan view of FIG. 17, two HBTs and a MIM capacitor betweenthe respective collector electrodes C thereof are shown, and the MIMcapacitor reduces the level of an odd-numbered harmonic. To therespective base electrodes B of the two HBTs, a differential pair ofinput signals are supplied. To each of the respective emitter electrodesE of the two HBTs, a ground voltage is supplied. Note that the two HBTshave a finger electrode structure in which the plurality of emitterelectrodes E and the plurality of collector electrodes C areinterdigitated with each other.

In the lower cross-sectional view of FIG. 17, a cross-sectionalstructure of a part of the HBT located on the left-hand side of theupper plan view of FIG. 17 is shown.

The HBT is formed over a GaAs compound semiconductor semi-insulatingsubstrate 42, and includes an N′-type subcollector layer 43, an N⁻-typecollector layer 44, a P⁺-type GaAs base layer 45, an N-type AlGaAsemitter layer 46, and an N⁺-type GaAs ohmic layer 47. The HBT alsoincludes a collector electrode 48, a base electrode 49, an emitterelectrode 50, a ground electrode 51 at the back surface of thesemi-insulating substrate 42, and a via hole 52. In particular, theemitter electrode 50 is assumed to be able to be coupled to the groundvoltage via the via hole 52 and the ground electrode 51. It is alsoassumed that the N⁻-type collector layer 44 of the HBT has a lowimpurity concentration, and the HBT has a high breakdown voltage. Inaddition, because the collector output capacitance of the HBT isreduced, and the resistance of an emitter-collector current path has arelatively large value, the output impedance also has a relatively largevalue.

<Specific RF Power Amplifier Module>

FIG. 18 is a view showing a configuration of a specific RF poweramplifier module used in a mobile phone terminal to which any of thevarious embodiments of the present invention shown in FIGS. 5 to 17described above is applied.

To an RF power amplifier module 100 shown in FIG. 18, high-band-side RFtransmission input signals Pin_HB in the DCS 1800/PCS 1900 bands andlow-band-side RF transmission input signals Pin_LB in the GSM 850/GSM900 bands are supplied.

The high-band-side RF transmission input signals Pin_HB are supplied toboth ends of a capacitor 101 and to both ends of the primary coil of aninput matching circuit 102. RF signals generated at both ends of thesecondary coil of the input matching circuit 102 and at both ends of acapacitor 103 are amplified by a first drive amplification stage 104 andby a second drive amplification stage 105. A differential pair ofamplified signals from the second drive amplification stage 105 aresupplied between both ends of a coil 106 and the respective gates ofN-channel LDMOS transistors 107 and 108 of a final-stage push-pull poweramplification circuit. The differential pair of amplified signalsgenerated between the respective drains of the N-channel LDMOStransistors 107 and 108 of the final-stage push-pull power amplificationcircuit is supplied to both ends of a capacitor 109 and to the primarycoil 1 (1A and 1B) of a transformer 110, and the power supply voltageVdd is supplied to the midpoint of the primary coil 1. As thetransformer 110, any of the transformers according to the variousembodiments of the present invention shown in FIGS. 5 to 10 can be used.To the secondary coil 2 of the transformer 110, the input terminal of anauxiliary output impedance matching circuit 111 formed of passiveelements which are an inductor 1111 and a capacitor 1112 is coupled.From the output terminal of the output impedance matching circuit 111, ahigh-band-side RF transmission output signal Pout_HB is generated. Apart of the high-band-side RF transmission output signal Pout_HB issupplied to the first input terminal of a power detector 300 via acapacitor 112.

The low-band-side RF transmission input signals Pin_LB are supplied toboth ends of a capacitor 201 and to both ends of the primary coil of aninput matching circuit 202. RF signals generated at both ends of thesecondary coil of the input matching circuit 202 and at both ends of acapacitor 203 are amplified by a first drive amplification stage 204 andby a second drive amplification stage 205. A differential pair ofamplified signals from the second drive amplification stage 205 issupplied between both ends of a coil 206 and the respective gates ofN-channel LDMOS transistors 207 and 208 of a final-stage push-pull poweramplification circuit. The differential pair of amplified signalsgenerated between the respective drains of the N-channel LDMOStransistors 207 and 208 of the final-stage push-pull power amplificationcircuit is supplied to both ends of a coil 209 and to the primary coil 1(1A and 1B) of a transformer 210, and the power supply voltage Vdd issupplied to the midpoint of the primary coil 1. As the transformer 210,any of the transformers according to the various embodiments of thepresent invention shown in FIGS. 5 to 10 can be used. To the secondarycoil 2 of the transformer 210, the input terminal of an auxiliary outputimpedance matching circuit 211 formed of passive elements which are aninductor 2111 and a capacitor 2112 is coupled. From the output terminalof the output impedance matching circuit 211, a low-band-side RFtransmission output signal Pout_LB is generated. A part of thelow-band-side RF transmission output signal Pout_LB is supplied to thesecond input terminal of the power detector 300 via a capacitor 212.

A bias control circuit 400 compares the level of a transmission powercontrol signal Vramp with the level of a power detection signal Vdetgenerated from the output of the power detector 300 to control the gainof the RF power amplifier such that the level of the power detectionsignal Vdet is equal to the level of the transmission power controlsignal Vramp. The control of the gain of the RF power amplifier iscontrolled based on the level of a bias voltage Vbias generated from thebias control circuit 400.

The power detector 300 and the bias control circuit 400 are formed by,e.g., a CMOS manufacturing process, and the active elements thereof areprimarily formed of short-channel MOS transistors. Since theshort-channel MOS transistors are lower in input power and input voltagesupplied thereto than the N-channel LDMOS transistors 107, 108, 207, and208 coupled to the transformers 110 and 210, a low-breakdown-voltagestructure can be employed. Therefore, in consideration of chip size, ahigh-speed operation characteristic, and the like, short-size channelMOS transistors having gate lengths smaller than those of the N-channelLDMOS transistors 107, 108, 207, and 208 are employed.

It has been assumed that the push-pull power amplification circuit isformed of N-channel LDMOS transistors, and the power detector 300 andthe bias control circuit 400 are formed of short-channel MOStransistors. However, the present invention is not limited thereto. Asactive elements used in the push-pull power amplification circuit,transistors having breakdown voltages higher than those of activeelements used in the power detector 300 and the bias control circuit 400are preferably employed.

While the invention achieved by the present inventors has beenspecifically described heretofore based on the embodiments thereof, thepresent invention is not limited thereto. It will be easily appreciatedthat various modification and changes can be made in the inventionwithout departing from the gist thereof.

For example, each of the RF power amplifiers according to the variousembodiments of the present invention is not only usable as an RF poweramplifier mounted in a mobile phone terminal, but also usable in a widerange as an RF power amplifier mounted in any of various RFcommunication apparatus such as a wireless LAN.

1. An RF power amplifier comprising: a first transistor and a secondtransistor each as an active device of a push-pull power amplificationcircuit; and a transformer as an output matching circuit of thepush-pull power amplification circuit, wherein a non-inverted inputsignal and an inverted input signal can be supplied respectively to aninput terminal of the first transistor and an input terminal of thesecond transistor, wherein the transformer has a primary coil and asecondary coil which are magnetically counted to each other, wherein oneend and the other end of the primary coil of the transformer are coupledrespectively to an output terminal of the first transistor and an outputterminal of the second transistor, wherein an output signal can begenerated from between one end and the other end of the secondary coilof the transformer, and wherein the primary coil of the transformerincludes at least a first coil and a second coil which are coupled inparallel between the output terminal of the first transistor and theoutput terminal of the second transistor, and each being magneticallycoupled to the secondary coil, wherein at least one of the first coiland the second coil can be supplied with a power supply voltage betweenthe output terminal of the first transistor and the output terminal ofthe second transistor, wherein the primary coil and the secondary coilof the transformer are formed of respective metal thin-film wires havingannular shapes, and each being formed in a flat shape over a surface ofa substrate, and wherein the metal thin-film wire forming the primarycoil of the transformer is formed to have a width larger than a width ofthe metal thin-film wire forming the secondary coil of the transformer.2. An RF power amplifier according to claim 1, wherein the metalthin-film wire forming the primary coil of the transformer and the metalthin-film wire forming the secondary coil of the transformer are formedaround the respective annular shapes, and wherein the primary coil andthe secondary coil are set to a predetermined ratio of turns to allowthe transformer to execute an output matching operation in accordancewith an impedance transformation ratio determined by the ratio of turns.3. An RF power amplifier according to claim 2, wherein the number ofturns of the secondary coil is set to generally be an integral multipleof the number of turns of the primary coil.
 4. An RF power amplifieraccording to claim 2, wherein the first and second coils of the primarycoil of the transformer are formed respectively of an outer metalthin-film wire and an inner metal thin-film wire, each having theannular shape, and wherein the secondary coil is formed of a middlemetal thin-film wire formed between the outer metal thin-film wire andthe inner metal thin-film wire.
 5. An RF power amplifier according toclaim 4, wherein the secondary coil formed of the middle metal thin-filmwire between the outer metal thin-film wire and the inner metalthin-film wire is formed with a plural number of turns.
 6. An RF poweramplifier according to claim 2, wherein the first coil, the secondarycoil, and the second coil are formed of a multilayer wiring structureformed over the surface of the substrate, and wherein, in the multilayerwiring structure, the secondary coil is interposed between the firstcoil and the second coil.
 7. An RF power amplifier according to claim 2,wherein the substrate is a semiconductor chip, wherein the firsttransistor and the second transistor are formed in the semiconductorchip, and wherein the transformer is formed as an on-chip transformer onthe semiconductor chip.
 8. An RF power amplifier according to claim 2,wherein the substrate having the transformer formed thereover is awiring substrate, wherein the first transistor and the second transistorare formed in a semiconductor chip, and wherein the transformer formedover the wiring substrate is electrically coupled to each of the firsttransistor and the second transistor which are formed in thesemiconductor chip by a coupling wire.
 9. An RF power amplifieraccording to claim 2, wherein the primary coil of the transformer isformed in a symmetrical shape.
 10. An RF power amplifier according toclaim 2, wherein each of the first transistor and the second transistoris a MOS transistor.
 11. An RF power amplifier according to claim 10,wherein the MOS transistor is an LDMOS transistor.
 12. An RF poweramplifier according to claim 2, wherein each of the first transistor andthe second transistor is a bipolar transistor.
 13. An RF power amplifieraccording to claim 12, wherein the bipolar transistor is a compoundsemiconductor heterojunction bipolar transistor.
 14. An RF poweramplifier according to claim 1, wherein the one end and the other end ofthe primary coil which are coupled to the first and second transistorsand the one end and the other end of the secondary coil between whichthe output signal can be generated are formed at mutually opposinglocations in the annular shapes.
 15. An RF power amplifier comprising: afirst transistor and a second transistor each as an active device of apush-pull power amplification circuit; and a transformer as an outputmatching circuit of the push-pull power amplification circuit, wherein anon-inverted input signal and an inverted input signal can be suppliedrespectively to an input terminal of the first transistor and an inputterminal of the second transistor, wherein the transformer has a primarymetal thin-film wire and a secondary metal thin-film wire, wherein theprimary metal thin-film wire and the secondary metal thin-film wire aremagnetically coupled to each other, and have respective annular shapeseach formed flat over a surface of a substrate, wherein one end of theprimary metal thin-film wire of the transformer is coupled to an outputterminal of the first transistor, while the other end of the primarymetal thin-film wire of the transformer is coupled to an output terminalof the second transistor, wherein an output signal can be generated frombetween one end and the other end of the secondary metal thin-film wireof the transformer, wherein the one end and the other end of the primarymetal thin-film wire of the transformer and the one end and the otherend of the secondary metal thin-film wire of the transformer are formedrespectively in a first portion and a second portion of each of theannular shapes which oppose each other, wherein, in the first portion ofthe annular shape, the one end and the other end of the primary metalthin-film wire of the transformer are disposed proximate to each otherwhile, in the second portion of the annular shape, the one end and theother end of the secondary portion thin-film wire of the transformer aredisposed proximate to each other, wherein the primary metal thin-filmwire of the transformer includes at least a first wire and a second wirewhich are coupled in parallel between the output terminal of the firsttransistor and the output terminal of the second transistor, and eachbeing magnetically coupled to the secondary metal thin-film wire,wherein at least one of the first wire and the second wire can besupplied with a power supply voltage between the output terminal of thefirst transistor and the output terminal of the second transistor, andwherein the primary metal thin-film wire of the transformer is formed tohave a width larger than a width of the secondary metal thin-film wireof the transformer.
 16. An RF power amplifier according to claim 15,wherein the primary metal thin-film wire of the transformer and thesecondary metal thin-film wire of the transformer are formed around therespective annular shapes, and wherein the primary metal thin-film wireand the secondary metal thin-film wire are set to a predetermined ratioof turns to allow the transformer to execute an output matchingoperation in accordance with an impedance transformation ratiodetermined by the ratio of turns.
 17. An RF power amplifier according toclaim 16, wherein the number of turns of the secondary metal thin-filmwire is set to generally be an integral multiple of the number of turnsof the primary metal thin-film wire.
 18. An RF power amplifier accordingto claim 17, wherein the first wire and the second wire of the primarymetal thin-film wire of the transformer are formed respectively of anouter metal thin-film wire and an inner metal thin-film wire, eachhaving the annular shape, and wherein the secondary metal thin-film wireis formed of a middle metal thin-film wire formed between the outermetal thin-film wire and the inner metal thin-film wire.
 19. An RF poweramplifier according to claim 18, wherein the secondary metal thin-filmwire formed of the middle metal thin-film wire between the outer metalthin-film wire and the inner metal thin-film wire is formed with aplural number of turns.
 20. An RF power amplifier according to claim 16,wherein the first wire, the secondary metal thin-film wire, and thesecond wire are formed of a multilayer wiring structure formed over thesurface of the substrate, and wherein, in the multilayer wiringstructure, the secondary metal thin-film wire is interposed between thefirst wire and the second wire.
 21. An RF power amplifier according toclaim 16, wherein the substrate is a semiconductor chip, wherein thefirst transistor and the second transistor are formed in thesemiconductor chip, and wherein the transformer is formed as an on-chiptransformer on the semiconductor chip.
 22. An RF power amplifieraccording to claim 16, wherein the substrate having the transformerformed thereover is a wiring substrate, wherein the first transistor andthe second transistor are formed in a semiconductor chip, and whereinthe transformer formed over the wiring substrate is electrically coupledto each of the first transistor and the second transistor which areformed in the semiconductor chip by a coupling wire.
 23. An RF poweramplifier according to claim 16, wherein each of the first transistorand the second transistor is a MOS transistor.
 24. An RF power amplifieraccording to claim 23, wherein the MOS transistor is an LDMOStransistor.
 25. An RF power amplifier according to claim 16, whereineach of the first transistor and the second transistor is a bipolartransistor.
 26. An RF power amplifier according to claim 25, wherein thebipolar transistor is a compound semiconductor heterojunction bipolartransistor.